Augmentation of soft tissue, e.g., skin, can be employed in many situations, including recovery from injury and for cosmetic or supporting purposes. For example, with normal aging, skin may become loose or creases can form, including, for example, nasal-labial folds, wrinkles, pitting and defects. Soft tissue augmentation can be used to correct defects such as creases and lines, and to counteract the effects of aging. It is desirable to even out irregularities of the skin permanently and without side effects. Soft tissue augmentation is achieved by the use of such materials as collagen, silicone, poly-lactic acid, polyethylene, polytetrafluoroethylene, and hydrogel-based polymer compositions. These materials can be in various forms depending on the use; for example, they can be in the form of thick solutions, gels or suspensions and used as implants or carriers for delivering the implants. Ideal materials for soft tissue augmentation should be sufficiently durable and remain in position and should not migrate from the implantation site.
Injectable dermal fillers are particularly desirable as a noninvasive intervention for reducing the appearance of skin defects. Injectable dermal fillers raise the skin within the skin defect, which is lower or deeper than the surrounding skin, causing the defect to fill to the same level as the surrounding skin, reducing the visibility of the defect.
U.S. Pat. No. 5,344,452 describes an alloplastic implant that is biocompatible and remains permanently at the injection site with substantially no side effects. The implant composition comprises solid particles having a smooth surface and being free from corners and edges such as a biocompatible solid in powder form, in particular polymethyl methacrylate (PMMA), in the form of microparticles. In certain aspects, the implant composition includes a physiologically acceptable suspending agent or carrier such as a biodegradable gelatine, water and/or alcohol. Such a dermal filler is commercially available as Artefill®.
While the compositions of U.S. Pat. No. 5,344,452 are well-suited for their intended purpose, it is desirable to design implant compositions with improved physical properties such as injectability and storage stability.